This invention relates to a synchrotron radiation (SR) source and more particularly to an industrial, compact SR source having an improved vacuum evacuation system which can attain vacuum evacuation performance suitable for this type of SR source.
As discussed in "Proceeding of the 5th Symposium on Accelerator Science and Technology" in the high energy laboratory reports, 1984, pp. 234-236, conventional accelerators and large-scale SR sources are known wherein bending sections, each of which deflects the orbit of a charged particle beam for causing the synchrotron radiation to be taken out of the source, are not collectively disposed in a relatively short range of the beam duct, but disposed with spaces between them where straight sections are disposed so that the bending sections are uniformly distributed as a whole in the beam duct.
Accordingly, sources of gases discharged from the interior wall surface of the charged particle beam bending duct under the irradiation of synchrotron radiation are substantially uniformly distributed along the orbit of the charged particle beam and besides gases discharged from the bending sections under the irradiation of the synchrotron radiation can be evacuated by not only built-in pumps installed inside the beam duct of the charged particle bending section but also vacuum pumps installed in an adjacent straight section, thereby ensuring that the charged particle beam bending duct can be maintained at high vacuum and a long lifetime of the charged particle beam can be maintained.
In compact SR sources for industrial purposes, however, because of a limited installation space and desirable cost reduction, the bending section for delivery of synchrotron radiation has to be laid concentratedly.
Taking a compact SR source comprised of two straight sections and two bending sections, for instance, it is necessary for one bending section to 180.degree. deflect the charged particle beam orbit and as a result, the amount of gases generated by each bending section under the irradiation of synchrotron radiation upon the interior wall surface of a charged particle beam bending duct is increased extremely, reaching about 10 times the amount of discharged gases generated by each bending section in the case of the large-scale SR source.
Accordingly, if the vacuum evacuation system of the large-scale SR source is directly applied to the compact SR source without alternation, then sufficient evacuation capability will not be obtained to thereby raise a problem that pressure in the charged particle beam bending duct rises and a desired lifetime of the charged particle beam can not be obtained.
Further, in the large-scale SR source, the bending angle is small, leading to a small spreading angle of the synchrotron radiation beam guided to the outside through SR guide duct and hence a crotch can be provided at an outlet window to the SR guide duct to restrict the SR beam in order to avoid the irradiation of the SR beam upon the interior wall surface of the SR guide duct and consequently prevent outgasing inside the SR guide duct under the irradiation of the SR beam, as discussed in "Nuclear Instruments and Methods 177", 1980, pp. 111-115. The provision of the crotch is very effective for differential evacuation between an SR beam line in which pressure is relatively high and the charged particle beam bending duct in which high vacuum must maintain.
Contrarily, in the industrial compact SR source, the bending sections for delivery of the synchrotron radiation are laid concentratedly because of a limited installation space and desirable cost reduction and hence the bending angle of each bending section is increased to a great extent.
In addition, since in the compact SR source the number of bending sections is limited, one bending section is provided with a plurality of SR guide ducts for guiding the synchrotron radiation to the outside. Because of the large spreading angle of the SR beam travelling through each of the guide ducts, the interior surface of each guide duct is irradiated with the SR beam to discharge a large amount of gases into each guide duct.
In the compact SR source, therefore, while the reduction in size limits the installation space of vacuum pumps, a large amount of gases are generated concentratedly, with the result that the charged particle beam bending duct can not be evacuated sufficiently, raising problems that residual gaseous molecules disturb the circular motion of the charged particle beam and a desired long lifetime of the beam cannot be obtained.